It is well known that, because of its high concentration of nitrate ions, ammonium nitrate (including double salts comprising ammonium nitrate) has important uses in the field of agriculture in general and fertilization in particular. However, it is also well known that ammonium nitrate, in many of the forms in which it has heretofore been commonly used, is relatively difficult and potentially hazardous to handle commercially in large amounts, and/or to store in great masses (such as occur in commercial warehouses and storage bins), especially for relatively long periods of time. Furthermore, it has been known that many of the forms of ammonium nitrate heretofore commonly used have had a tendency to detonate under relatively mild conditions, and have therefore sometimes been abused and misused as an explosive material.
Additionally, because of its detonation potential, many processes for producing such materials are used under conditions that make the process more susceptible than is desirable to detonation hazard. In addition, certain prior processes utilize conditions that are relatively expensive to operate and/or are less efficient than is desired.
For example, one method commonly used is based on the formation of a melt comprising ammonium nitrate, ammonium sulfate and water. That process is disclosed in U.S. Pat. No. 6,689,181, the subject matter of which is incorporated herein by reference. The method disclosed in '181 comprises charging materials comprising ammonium sulfate particles, ammonium nitrate and water to a melting vessel using a molar ratio of ammonium sulfate to ammonium nitrate of about 0.9:1 to about 1.1:1. '181 discloses that the water should be charged to the vessel in an amount that is more than 2 wt % and up to about 10 wt % of the charged materials. The charge is then processed by melting the ammonium nitrate and dissolving at least a portion of the ammonium sulfate particles at a temperature of about 180° C. to about 210° C. The melt is then reacted at a temperature of about 180° C. to about 210° C. The reaction product is then solidified by cooling at a rate of greater than 100° C. per minute.
A disadvantage of '181 is that relatively high temperatures (180° C. to 210° C.) are specified for forming the melt of ammonium nitrate and ammonium sulfate and these temperatures begin to approach the decomposition temperature of ammonium nitrate. Decomposition reactions result in the production of nitrogen oxides in the melt and, therefore, they can cause the resulting solid to have increased porosity and softness, which is generally a disadvantage when producing a relatively non-hazardous fertilizer. Moreover, at such relatively high processing temperatures, the chances of unwanted decomposition of nitrates with accompanying formation of nitrogen oxides increase considerably. This causes loss of nitrogen in the final product. Also, the relatively high decomposition possibility increases the chances of violent reaction, deflagration, and/or explosion during processing, which increases the risk to the health, life and/or property of plant works and residents of the surrounding communities.
Another disadvantage in '181 relates to the relatively long reaction times and rapid cooling rates to achieve solidification. The relatively long reaction time at relatively high reaction temperature also increases the risk of decomposition and the long reaction times, together with rapid cooling rates, can increase the cost of the process.
Another melt-based process is disclosed in EP1923376. The process involves producing ammonium nitrate sulfate in a multistage reaction system which comprises a mixing stage and a granulation stage followed by a drying stage. Ammonium nitrate sulfate suspension in '376 is said to be prepared in a continuous process by feeding ammonium nitrate melt, dolomite and ammonium sulfate into the reactor. Dolomite addition in the reaction system is said to stabilize ammonium nitrate and prevent its decomposition in the reaction medium.
A deficiency of '376 relates to the use of water in a melt at below 1% by weight. This feature, as well as other features, is detrimental in that the process is not conducive to the formation of the desirable 1:2 ANS double salt.